It is widely known that a coke with high strength is desirable for use as a raw material in the production of pig iron in a blast furnace. A coke with low strength would disintegrate in the blast furnace and deteriorate the gas permeability of the blast furnace, which leads to unstable production of pig iron.
In the case of producing coke for ironmaking by carbonizing coal in a horizontal chamber coke oven, the strength of produced coke is affected by the conditions such as a method for selecting coal for cokemaking, a preparation method, carbonization conditions, quenching conditions, post-treatment conditions. Among these conditions, conditions relating to facilities or operation are limited due to equipment and it is difficult to significantly change the conditions. Therefore, the selection of coal for cokemaking is recognized as the most important factor in controlling the coke properties.
Various methods are known for blending coals to produce a coke with desired strength, including a method described in Non Patent Literature 1. All of these method comprises predicting the strength of produced coke based on the properties of the coals to be blended and determining a blend of coals to provide high strength.
However, it is known that the conventional methods for determining the blend of coals provide inaccurate estimation of coke strength. In this case, the influence of an effect referred to as the “compatibility between coals” is conceivable. The “compatibility between coals” refers to the interaction between a plurality of coals in a coal blend. It is known that additivity does not hold between the strength of coke obtained from each coal in the coal mixture and the strength of coke obtained from the coal mixture because of the compatibility between the coals as disclosed in, for example, Patent Literature 1 and Non Patent Literature 2. If a mechanism creating the “compatibility” effect is clear, then coke with high-strength can be produced using a combination of compatible coals. However, conventional techniques have not clarified what creates the “compatibility” effect. It is unknown that what coal mixture should be supplied in order to achieve a combination of compatible coals or how to obtain such a coal mixture.